This invention relates to an apparatus and method for foaming a liquid/gas mixture.
Foamed liquids are often desirable in many applications such as, for example, the production of oil, gas or geothermal liquids from the earth. For example, a foamed cement slurry is often introduced in the annulus between the outer surface of a casing and the inner surface of a well to secure the casing in the well. The foam is usually produced by mixing a gas, such as nitrogen, with the cement slurry in a manner to form a foam and then introducing the mixture into the well.
In these arrangements, it is desirable to create a fine, textured foam by creating relatively high shearing forces on the liquid/gas mixture. However, in connection with cementing relatively shallow wells, the ultimate pressure of the cement slurry is relatively low and therefore the mass of the gas required to lighten the cement is also relatively low, which reduces the energy available to create the high shearing forces. Also, some previous attempts to form foamed cement slurries include discharging a gas, such as nitrogen, at a very high velocity, into a tee into which a cement is introduced in a flow path extending ninety degrees to the flow path of the nitrogen. However, the nitrogen must be discharged into the cement slurry at very high velocities to create shearing forces sufficient to produce a fine textured foam which renders it difficult to control the direction of the resulting nitrogen/cement slurry mixture. Producing the high pressure gas requires special and expensive pumping equipment not normally used in cementing operations.
Therefore, according to an embodiment of the invention, a mixture of gas and a liquid is introduced into a vessel at a predetermined velocity and passes through a passage in the vessel. The flow of the mixture through the passage is increased to increase the velocity of the mixture and cause corresponding shearing forces on the mixture to create a turbulence and form foam from the mixture. The restrictor can be moved in the passage to vary the amount of restriction and therefore the amount of the foam.